The group of elements known as the actinides is the elements from actinium, atomic number 89, to lawrencium, atomic number 103. All the elements in this series can resemble actinium in their chemical and electronic properties so that they form a separate group of elements within the periodic table.
All actinides are metals and all are radioactive. They emit energy in the form of alpha particles, beta particles, or gamma rays and by emitting these particles or photons, the actinide atom loses protons and as a result becomes another element with a lower atomic number. The actinides undergo radioactive decay at different rates, that is, they have different half-lives. The elements with the higher atomic numbers generally have short half-lives and rapid radioactive decay. Some actinides with lower atomic numbers have half-lives that can be thousands or even millions of years.
The two actinides of most general interest are uranium and plutonium, uranium being a naturally occurring element whereas plutonium is a created element.
Environmental contamination by actinides is a major concern around facilities that engage in activities that use or produce actinides or facilities where nuclear stockpiles are maintained. The actinides such as uranium, neptunium, plutonium, and americium are major contributors to the long-term activity of nuclear waste which must be stored at remote sites. In order to determine the long-term safety of storage sites, testing of soil samples is of prime interest in evaluating the safety of such storage sites.
Of the actinides and their isotopes, plutonium is perhaps the most complex element in the periodic table because it may assume one of six different forms or phases, each with a different density and volume. Because of plutonium's behavior, it receives special concern for not only its handling but for its detection. A very large sample size is not needed to adequately measure uranium in soil due to its relatively high level compared to other actinides such as plutonium and americium; and, because of the difficulty of detecting plutonium; a larger soil sample is required.
However, in a large soil sample the amount of uranium that is present interferes with plutonium and americium detection methods. As a result, steps must be taken to prevent uranium interference in plutonium and americium chemical recoveries.
Accordingly, it is an object of the present invention to provide a method for detecting plutonium, americium, and curium isotopes in relatively large soil samples.
In U.S. Pat. No. 5,190,881 to Terry T. McKibbon a process is described for analyzing human waste for actinides. Uranium accompanies the plutonium through the extraction process but is separated from the plutonium in the cerium fluoride precipitation step, the uranium staying in the filtrate. The uranium can be recovered by the addition of titanous chloride and more cerium carrier to the fluoride filtrate. The fractions are electrodeposited or carried by cerium fluoride on filter paper and analyzed by alpha spectrometry for isotope identification and quantification.
Accordingly, it is another object of the present invention to provide an effective and simple method for analyzing samples for actinides by employing cerium fluoride precipitation.
The above and additional objects are achieved by this invention which is described below.